CLIAMS:1. A variable ratio steering gear comprising:
a nut configured with a rack on its one side, wherein teeth of the rack are configured to have variable pitch such that pitch line of the rack teeth is variable from basic pitch of a given module; further wherein said rack teeth have depth that increases towards the two ends of the rack from center, and wherein tooth profile is modified from that of a basic rack profile with increased pressure angle at the ends as compared to pressure angle at the center of the rack; and
a rocker shaft with a sector gear, wherein said sector gear is operatively coupled with said rack and configured to have a constant pitch radius, and wherein the sector gear is placed ex-center from the axis of rotation of the rocker shaft.
2. The variable ratio steering gear of claim 1, wherein the sector gear and the rack are configured to provide a variable gear ratio that increases towards the two ends as compared to center.
3. The variable ratio steering gear of claim 1, wherein the variable ratio steering gear further comprises a worm shaft configured with a worm, wherein said nut is operatively coupled to the worm shaft through recirculating balls such that rotation of the worm shaft causes linear movement of the nut.
4. The variable ratio steering gear of claim 1, wherein the worm shaft, the nut and the rocker shaft are configured within a housing, wherein the rocker shaft is placed transverse to the worm shaft with the teeth of the rocker shaft in engagement with the rack configured on the nut.
5. A vehicle fitted with a variable ratio integral power steering gear, said steering gear configured to require uniform hydraulic pressure from one lock position to other lock position, and comprising:
a nut configured with a rack on its one side, wherein teeth of the rack are configured to have variable pitch such that pitch line of the rack teeth is variable from basic pitch of a given module; further wherein said rack teeth have depth that increases towards the two ends of the rack from center, and wherein tooth profile is modified from that of a basic rack profile with increased pressure angle at the ends as compared to pressure angle at the center of the rack; and
a rocker shaft with a sector gear, wherein said sector gear is operatively coupled with said rack and configured to have a constant pitch radius, and wherein the sector gear is placed ex-center from the axis of rotation of the rocker shaft.
6. The vehicle of claim 5, wherein the sector gear and the rack are configured to provide a variable gear ratio that increases towards the two ends as compared to center.
7. The vehicle of claim 5, wherein the steering gear further comprises a worm shaft configured with a worm, wherein the nut is operatively coupled to the worm shaft through recirculating balls such that rotation of the worm shaft causes linear movement of the nut.
8. The vehicle of claim 5, wherein the worm shaft, the nut and the rocker shaft are configured within a housing, wherein the rocker shaft is placed transverse to the worm shaft with the teeth of the rocker shaft in engagement with the rack configured on the nut.
9. The vehicle of claim 5, wherein the nut and the housing are configured to form two hydraulic chambers on two sides of the nut; further the nut incorporates valves to sense direction of rotation of the worm and selectively direct a pressurized hydraulic fluid to one or other of the two chambers to assist in movement of the nut.
10. The vehicle of claim 5, wherein the steering gear further comprises a rocker arm configured on the rocker shaft, the rocker arm operatively coupled to a pair of steered wheels of the vehicle.
,TagSPECI:TECHNICAL FIELD
[0001] The present disclosure generally relates to the field of automobile. More particularly it relates to a variable ratio integral power steering gear assembly.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art
[0003] All automobiles typically exhibit a tendency wherein effort required to turn steered wheels increases as they are turned away on either side from straight ahead position. This is primarily due to steering linkages connecting/transmitting motion from steering gear to the steered wheels. These steering linkages by virtue of their geometry tend to provide lower mechanical advantage as the steered wheels are turned away from straight ahead (center) position. Other contributing factor for higher effort away from straight ahead position is on account of inherent tendency of the wheels to return to straight ahead position which increases as they move away from straight ahead position. This tendency is built into the vehicles by design to generate a desirable self-centering action.
[0004] Therefore, before the advent of power steering gears there was a practice, especially in respect of heavier vehicles, to have steering gears that provided higher steering gear ratio towards the ends as compared to center so that the effort required by drivers to steer the vehicle does not go beyond human capabilities. The practice continued even after introduction of power steering systems under the belief that the drivers should have the same feel of steering irrespective of whether he is driving a vehicle with manual steering or power steering. The trend reversed after power steering became a norm for all vehicles and steering gears that provided lower gear ratio towards the ends were used so that total number of steering wheel turns to turn steering from one extreme (lock position) to other could be reduced. This was an attractive alternative as it provided efficiency in certain operations such as parking.
[0005] Power steering gears that provide lower gear ratio towards the ends, need higher hydraulic pressure to operate as reduced gear ratio required higher effort which has to be met by higher power assistance. Other alternative to higher hydraulic pressure is to increase piston size and in either case equipment size had to be increased. It is also apparent that these systems do not utilize the power equipment most effectively since torque input and output requirements are not balanced as they are in systems that have higher gear ratio towards the ends. In the center position of the steered wheels, where steering torque requirements are least, steering ratio is greatest. Conversely, toward the end positions of the steered wheels, where the torque requirements are generally greatest, the steering ratio is least. Therefore it is desirable to have a configuration that provides higher gear ratio towards the ends as compared to center as such a system operates at more or less uniform hydraulic pressure throughout the operating range of the steering gear, minimizes the hydraulic pressure requirement and reduces the rating and size of the hydraulic system.
[0006] There are a number of disclosures on variable ratio integral power steering gear. For example US patent 3741074 discloses a variable ratio integral power steering gear that provides higher gear ratio towards the ends than at center. However, it uses a variable pitch sector gear whose pitch radius increases from the center to the end thereof. Further it incorporates a constant (basic module) pitch rack with variable depth. The design is not amenable to high mechanical efficiency and also needs larger number of teeth on the sector gear.
[0007] US patent 4255980 discloses another such steering gear assembly that incorporates a sector gear with constant pitch radius but its rack is configured to provide lower gear ratio towards the ends than at center.
[0008] There is therefore need for a variable ratio integral power steering gear that provides higher gear ratio towards the ends than at center, offers high mechanical efficiency, and is easy to manufacture.
[0009] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0010] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0011] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0012] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0013] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION
[0014] An object of the present disclosure is to provide an integral power steering gear that operates at optimum hydraulic pressure throughout its range of operation.
[0015] Another object of the present disclosure is to provide a variable ratio integral power steering gear that has higher gear ratio towards the ends than at center.
[0016] Another object of the present disclosure is to provide a variable ratio integral power steering gear that provides high mechanical efficiency.
[0017] Another object of the present disclosure is to provide a variable ratio integral power steering gear that is easy to manufacture.

SUMMARY
[0018] Aspects of present disclosure relate to a steering gear. In an aspect the disclosure provides an integral power steering gear that operates at optimum hydraulic pressure throughout its range of operation. In another aspect the disclosed steering gear has higher gear ratio towards two ends as compared to center position such that the steering gear ratio generally matches the effort required to turn steered wheels that increases as they are turned away on either side from straight ahead (center) position thus needing generally uniform power from one lock position to other lock position.
[0019] In an embodiment, the disclosed variable ratio integral power steering gear incorporates a worm shaft having a worm, a nut on the worm shaft in engagement with the worm for axial movement upon rotation of the worm shaft. The nut can have a rack on one side, a rocker shaft configured transverse to the worm shaft, and a sector gear mounted on the rocker shaft and having teeth in engagement with teeth of the rack.
[0020] In an embodiment, the rack is a variable pitch rack such that pitch line of the rack teeth is variable from basic pitch of a given module and the rack teeth have depth that increases towards the two ends of the rack from the center of the rack.
[0021] In an embodiment, the rack tooth profile is modified from that of a basic rack profile with 25 degree pressure angle at the center to an increased pressure angle of 40 degree at the ends to provide for improved contact efficiency and variable ratio contact radius.
[0022] In an embodiment, pitch radius of the sector gear is constant and placed ex-center from the axis of rotation of the rocker shaft.
[0023] In an embodiment, the nut and the rocker shaft configured with rack and the sector gear respectively in accordance with above embodiments can provide a variable gear ratio that increases towards the two ends as compared to center. In an aspect the increase in the gear ratio can generally match the increase in effort required to turn steered wheels as they are turned away on either side from straight ahead (center) position thus resulting in generally a uniform power requirement during operation of the steering on either side from straight ahead position.
[0024] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components

BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0026] FIG. 1 illustrates an exemplary longitudinal cross sectional view of a variable ratio integral power steering gear in accordance with embodiments of the present disclosure.
[0027] FIG. 2 illustrates an exemplary lateral cross sectional view of the variable ratio integral power steering gear in accordance with embodiments of the present disclosure.
[0028] FIG. 3 illustrates an exemplary lateral cross sectional view of the variable ratio integral power steering gear indication hydraulic valves in accordance with embodiments of the present disclosure.
[0029] FIG. 4 illustrates an exemplary cross sectional view of the nut configured with rack in accordance with embodiments of the present disclosure.
[0030] FIG. 5 illustrates an exemplary cross sectional view of the roker shaft configured with sector gear in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION
[0031] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0032] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0033] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0034] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0035] Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0036] Embodiments of the present disclosure relate to a variable ratio integral power steering gear (also referred to as steering gear hereinafter) that can operate at optimum hydraulic pressure throughout its range of operation. In an embodiment the disclosed steering gear has higher gear ratio towards two ends as compared to center position such that the steering gear ratio generally matches the effort required to turn steered wheels and thus can meets the requirement of applications where the effort required to turn the steered wheels increases as they are turned away on either side from straight ahead (center) position. The disclosed steering gear therefore helps in achieving generally uniform power requirement from one lock position to other lock position.
[0037] It is to be understood that though the embodiments of the present disclosure have been described with reference to an integral power steering gear, it is possible to implement them in a manual steering gear as well and such an application is well within the scope of the present disclosure.
[0038] In an embodiment, the disclosed variable ratio integral power steering gear can incorporate a worm shaft having a worm, a nut on the worm shaft in engagement with the worm for axial movement upon rotation of the worm shaft. The engagement means can be recirculating balls configured between the worm and the nut. The nut can have a rack configured on its one side. There can be a rocker shaft configured transverse to the worm shaft, and a sector gear mounted on the rocker shaft and having teeth in engagement with teeth of the rack.
[0039] In an embodiment, the rack is a variable pitch rack such that pitch line of the rack teeth is variable from basic pitch of a given module and the rack teeth have depth that increases towards the two ends of the rack from the center of the rack.
[0040] In an embodiment, the rack tooth profile is modified from that of a basic rack profile with 25 degree pressure angle at the center to an increased pressure angle of 40 degree at the ends to provide for improved contact efficiency and variable ratio contact radius.
[0041] In an embodiment, pitch radius of the sector gear is constant and placed ex-center from the axis of rotation of the rocker shaft.
[0042] In an embodiment, the nut and the rocker shaft configured with rack and the sector gear respectively in accordance with above embodiments can provide a variable gear ratio that increases towards the two ends as compared to center. In an aspect the increase in the gear ratio can generally match the increase in effort required to turn steered wheels as they are turned away on either side from straight ahead (center) position thus resulting in generally a uniform power requirement during operation of the steering on either side from straight ahead position.
[0043] Referring now to FIG. 1, an exemplary longitudinal cross sectional view of a variable ratio integral power steering gear 100 is disclosed in accordance with the various embodiments herein. The variable ratio integral power steering gear 100 can comprise of a worm shaft 102 having a worm 104, a nut 106 on the worm shaft 102 in engagement with the worm for axial movement upon rotation of the worm shaft. The engagement means can be recirculating balls 108 configured between the worm and the nut. The nut 106 can have a rack 110 configured on its one side. Also shown in FIG. 1 is cross section of a sector gear 112 that can be configured on a rocker shaft configured transverse to the worm shaft 102.both the worm shaft 102 along with nut 106 and rocker shaft can be configured within a housing 114 wherein the nut 106 can be configured within the housing 114 in a cylindrical bore so as to define two chambers 116 and 118 on either side of the nut 106. The nut can have sealing means such as 120 that can fluidically isolate the two chambers 116 and 118.
[0044] In an embodiment the chambers 116 and 118 can be configured to receive supply of a pressurized hydraulic fluid on requirement basis, such that the pressurized hydraulic fluid can apply pressure on the nut 102 in a selective manner to power nut’s 106 movement in lateral direction along the axis of the worm shaft 102.
[0045] In an embodiment of application, the worm shaft 102 can be operatively coupled to a steering wheel by suitable means. When the steering wheel is turned the nut 106 because of its engagement with worm 104 (configured on the worm shaft 102) by means of recirculating balls 108, can experience lateral motion along the axis of the worm shaft 102. The axial motion of the nut 106 can result in rotational motion of sector gear 112 because of engagement of the two through the teeth of rack 110 configured on the nut 106 and teeth of sector gear 112. The mechanical advantage associated with the above motion can be the gear ratio between the worm shaft 102 and the sector gear 112.
[0046] In an embodiment the rack 110 and the sector gear 112 can be configured to provide a variable gear ratio such that the ratio towards the end of movement of the nut 106 and sector gear 112 on either side, is greater than the gear ratio in the center position.
[0047] FIG. 2 illustrates an exemplary lateral cross sectional view 200 of the variable ratio integral power steering gear 100 in accordance with embodiments of the present disclosure. Shown therein is a rocker shaft 202 that can be configured with the sector gear 112 as shown. Also shown in view 200 is the nut 106 that can be in engagement with the sector gear 112 through their respective teeth. The variable ratio integral power steering gear 100 can further incorporate input and output ports 204 and 206 respectively for the pressurized hydraulic fluid.
[0048] In an embodiment of application, the rocker shaft 202 can be operatively coupled to a rocker arm which in turn can be connected to steering linkages to transmit steering action from the steering gear 100 to the steered wheel of a vehicle. Thus, as the steering wheel is turned to either left or right, the rocker shaft 202 also rotates in one or other direction causing steering linkages to turn the steered wheels of the vehicle in the corresponding direction.
[0049] FIG. 3 illustrates an exemplary lateral cross sectional view 300 of the variable ratio integral power steering gear 100 indication hydraulic valves in accordance with an embodiment of the present disclosure. Shown therein are the worm 104, the nut 106 and rocker shaft 202 configured within the housing 114. As shown the nut 106 can be configured with a set of valves such as 302, 304 and 306 configured to sense the direction of rotation of the worm shaft 102 and selectively direct flow of the pressurized hydraulic fluid to either chamber 116 or chamber 118 so that the pressurized hydraulic fluid meets the desired effort requirement to turn the steered wheels.
[0050] FIG. 4 illustrates an exemplary cross sectional view 400 of the nut 106 configured with rack 110 in accordance with an embodiment of the present disclosure. As shown in the view 400 the nut 106 can be configured with the rack 110 on one side. In an embodiment, the rack can be a variable pitch rack such that pitch line of the rack teeth is variable from basic pitch of a given module.
[0051] In another embodiment the teeth away from center such as 402 can have higher depth compared to tooth at center such as 404. As shown the depth of the teeth 402 when measured using a ball of appropriate diameter, can be ‘Y’ in terms of position of the ball from center of the nut 106. As against this the depth of the tooth 404 when measured using a ball of same diameter, can be ‘X’ in terms of position of the ball from center of the nut 106.
[0052] In an embodiment rack profile can be modified as shown in the view 400 for better efficiency of contact between the rack 110 and sector gear 112.
[0053] In an embodiment, the rack tooth profile is modified from that of a basic rack profile with 25 degree pressure angle at the center to an increased pressure angle of 40 degree at the ends to provide for improved contact efficiency and variable ratio contact radius.
[0054] FIG. 5 illustrates an exemplary cross sectional view 500 of the rocker shaft 202 configured with sector gear 112 in accordance with embodiments of the present disclosure. In an embodiment, pitch radius 502 of the sector gear 112 can be constant and placed ex-center from the axis of rotation of the sector shaft as shown in the view 500.
[0055] In an embodiment the constant pitch sector gear 112 can be manufactured by shaping or hobbing process and thus makes the manufacture of the disclosed variable ratio integral power steering gear easy with corresponding cost benefits.
[0056] In an embodiment, the nut and the rocker shaft configured with rack and the sector gear respectively in accordance with above embodiments can provide a variable gear ratio that increases towards the two ends as compared to center. In an aspect the increase in the gear ratio can generally match the increase in effort required to turn steered wheels as they are turned away on either side from straight ahead (center) position thus resulting in generally a uniform power requirement during operation of the steering on either side from straight ahead position.
[0057] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0058] The present disclosure provides an integral power steering gear that operates at optimum hydraulic pressure throughout its range of operation.
[0059] The present disclosure provides a variable ratio integral power steering gear that has higher gear ratio towards the ends than at center.
[0060] The present disclosure provides a variable ratio integral power steering gear that provides high mechanical efficiency.
[0061] The present disclosure provides a variable ratio integral power steering gear that is easy to manufacture.